When drilling a well, a bore is formed in the earth and extended via rotation of a drill bit, which is attached at the end of a string of tubulars. The drill bit can be rotated by rotating the attached tubular string, e.g., using a rotatable member engaged with the tubular string at the surface, though during some operations—most notably directional drilling operations—the drill bit is rotated using a downhole motor (e.g., a progressive cavity positive displacement pump). Typical downhole motors rotate an associated drill bit responsive to the flow of drilling fluid through the motor. Specifically, a movable rotor, positioned within a stator housing, rotates due to the pressure of the drilling fluid applied to the rotor. The rate at which the borehole can be extended, often referred to as the ROP (rate of penetration), can be optimized by providing a significant amount of weight to the drill bit (termed the weight-on-bit (WOB)).
In operations where a downhole motor is used, operators may often attempt to increase the ROP by providing drilling fluid into the tubular string in excess of the tolerance of the downhole motor. If the motor lacks sufficient horsepower or momentum to continue the drilling operation, the motor may stall. In other situations, the characteristics of the formation or damage to the drill bit can contribute to stalling of the motor. If the differential pressure across the motor becomes extremely high, which can readily occur during a stall, the continued provision of drilling fluid into the motor can cause severe damage to the motor—primarily to the rubber, composite, and/or elastomeric liner of the stator housing, as well as to other power transmission components (e.g., the flex shaft or tie-rod).
Stalls can often be prevented, by an operator, if a signal or indication of the pressure differential is communicated to the surface; however, lack of operator responsiveness and/or the incentive to maximize the ROP in spite of the risk of a stall can hinder the effectiveness of a human response. Additionally, in instances where formations vary greatly, little can be done to prevent damage to the drill bit, mud motor, and/or associated components in the bottomhole assembly. Mechanical devices can be used to reduce the damage caused by a stall, e.g., by detecting conditions indicative of a stall or conditions that may potentially lead to a stall, such as reduced motor speed and/or pressure in the tubular spring, then diverting the flow of fluid away from the motor, but mechanical devices are prone to damage and/or failure. Additionally, mechanical forces, such as those caused by the rapid extension of springs, can be significant, causing damage to threaded connections, tools, and other components, interfering with measurements in instruments and sensors in the bottomhole assembly, and potentially un-torqueing connections in the tubular string. Mechanical devices are also limited by size constraints, and are often unsuitable for use within smaller strings and wellbores. Further, many mechanical devices require use of a physical object that can obstruct the bore of the tubular string, such as a ball or dart, that must later be removed and/or otherwise overcome when it is desired to actuate other ball-activated tools located downhole from the device.
A need exists for devices and methods usable to control the flow of drilling fluid and bypass a downhole motor that can be activated and reset by a pressure differential to reduce the likelihood of a stall and/or minimize damage to components should a stall occur.
A need also exists for devices and methods usable to bypass fluid into the annulus about a tubular string to assist in moving cuttings and solids to the surface to improve the condition of the wellbore, while bleeding excess pressure from the tubular string.
A further need exists for devices and methods that can control the flow of drilling fluid to a downhole motor while leaving the central bore of the tubular string generally unobstructed, and can selectively allow split flow (e.g., partial flow toward the drill bit) to enable rotation of the bit, e.g., via the motor mount.
Embodiments usable within the scope of the present disclosure meet these needs.